1. Field of the Invention
The present invention relates to a zoom lens system having a camera shake compensating function, and more specifically, to a zoom lens system having a camera shake compensating function being suitable for use in lens-shutter cameras, said zoom lens system being capable of preventing image blurs due to camera shake (for example, vibrations caused when photographing is performed with the camera being hand held).
2. Description of the Prior Art
Conventionally, failures in photographing have resulted mostly from camera shake and being conducted in an out-of-focus state. In recent years, however, the automatic focusing mechanism has been employed in most cameras and as the focusing accuracy of the automatic focusing mechanism improves, the failure in photographing due to an out-of-focus state has been virtually solved. On the other hand, lens systems which come standard on cameras have shifted from fixed focal length lens systems to zoom lens systems. As a result, at present, it is no exaggeration to say that failures in photographing are caused by camera shake. For this reason, a camera shake compensating function is indispensable to zoom lens systems.
With the intention of solving this problem, various zoom lens systems have been proposed. For example, Japanese Laid-open Patent Application H8-101362 discloses a five-unit zoom lens system of positive, negative, positive, positive, negative configuration in which a fourth lens unit is subdivided into three units and the central lens unit of the three is parallelly decentered to perform camera shake compensation. Japanese Laid-open Patent Application No. H6-265827 discloses a three-unit zoom lens system of positive, positive, negative configuration in which a second lens unit is subdivided into front and rear lens units and the rear lens unit is parallelly decentered to perform camera shake compensation. Japanese Laid-open Patent Application No. H7-318865 discloses a five-unit zoom lens system of positive, negative, positive, positive, negative configuration in which a fourth lens unit is parallelly decentered to perform camera shake compensation. Japanese Laid-open Patent Application No. H6-265856 discloses a two-unit zoom lens system of positive, negative configuration in which a first lens unit is parallelly decentered to perform camera shake compensation. Japanese Laid-open Patent Application No. H6-130203 discloses a three-unit zoom lens system of positive, positive, negative configuration in which a second lens unit comprises a lens unit having a transparent liquid sealed therein and the lens unit is inclined to perform camera shake compensation.
However, in the zoom lens systems disclosed in Japanese Laid-open Patent Applications Nos. H8-101362, H6-265827 and H7-318865, since the movement amount of the camera shake compensating lens unit varies according to the focal length, it is necessary to provide means for detecting the focal length during zooming to calculate the camera shake compensation drive amount. This increases cost. Since the movement of the axial image point and the movement of the off-axial image point are different from each other during camera shake compensation, the off-axial image point largely moves, so that excellent optical performance cannot be obtained. In the zoom lens system disclosed in Japanese Laid-open Patent Application No. H6-265856, although the first lens unit is parallelly decentered, magnification can be varied only up to approximately 2.times. since there are only two zooming units, so that a higher magnification cannot be achieved. In the zoom lens system disclosed in Japanese Laid-open Patent Application No. H6-130203, when the lens unit having a transparent liquid sealed therein is inclined to perform camera shake compensation, axial chromatic aberration is generated. Since it is difficult to correct the axial chromatic aberration, excellent imaging quality cannot be obtained.